Two-cycle internal combustion engines are well known in the art and have been used for many and varied purposes. One specific variation of the two-cycle engine utilizes two cylinders each having first and second opposed pistons whose surfaces are moved together and apart to define a combustion chamber. The first pistons of each cylinder are operatively connected at opposite ends of a pivotally mounted rocker arm, the second pistons of each cylinder also being operatively connected to a second rocker arm. The sides of the pistons in such an engine alternately open and close input and transfer ports whereby air or an air/fuel mixture may be entered into the piston-defined combustion chamber and the combustion products removed therefrom. (Hereinbelow, reference to "air" will comprise an "air-fuel" mixture whenever appropriate.) However, the efficiency of conventional internal combustion engines varies as a function of engine r.p.m., manifold pressure, altitude, octane rating, and many other parameters. Consequently, engines are designed so that their peak efficiency occurs under certain predetermined conditions which are representative of anticipated or probable operating parameters. If the engine is operated under conditions different from this predetermined set of conditions, engine efficiency drops and the net effect is more fuel consumption.
Three basic factors contribute to reduced efficiency as the engine is operated under conditions apart from the predetermined conditions. The first factor is the closing of the exhaust port either too early or too late with respect to the opening of the transfer port. In a two-cycle engine, the exhaust port is opened prior to opening of the transfer port for pressure equalization, the opening of the transfer port then forcing combustion products out the exhaust port. As one can appreciate, an optimum time for closing the exhaust port would be at the moment when the incoming air just reaches the exhaust port and has forced the last of the combustion products out through the exhaust port. If the exhaust port is closed prematurely, all of the prior combustion products will not be expelled, whereas if it is closed too late, some of the fuel within the air will be wasted. In conventional engines, this optimum closing of the exhaust port only occurs under one set of operating conditions. Another factor contributing to reduced efficiency in conventional engines is that the stroke, that is the maximum distance apart the pistons attain, is fixed. As is well known, the stroke determines the compression ratio of the engine, that is, the ratio of the pressure internal to the combustion chamber at the time of combustion with respect to the outside or manifold pressure. Therefore as the outside pressure decreases below an assumed design pressure due to a reduced throttle setting, increased engine speed, or increased altitude, the pressure in the combustion chamber at the time of combustion decreases. This lower pressure results in a less than optimum fuel burning efficiency. A third factor contributing to reduced efficiency in combustion engines is a change in volume of the combustion chamber during combustion, the change occurring because of piston travel during the combustion process. This volume change affects the efficiency of combustion and results in a less efficient use of the fuel. All of the above disadvantages of conventional engines combine to define an engine having less overall fuel efficiency than that potentially achievable.
The present invention provides a two-cycle, opposed cylinder internal combustion engine which is more efficient than any conventional engine. The engine consists of a pair of cylinders each of which has first and second pistons that act oppositely in a predetermined phase relationship so that their facing surfaces are moved together and apart to define a stroke length and to at least partially define a combustion chamber. Also the piston side surfaces alternately block and unblock transfer ports and exhaust ports as they move together and apart. Means are provided for providing fuel to the combustion chamber through the transfer ports or for injection directly into a remote combustion chamber. A pivotally mounted first rocker arm is provided, the arm having opposite ends connected to a first piston in each cylinder for reciprocal movement thereof. A means connected to the second pistons for reciprocal movement thereof is also provided, in a specific embodiment the means being a second rocker arm.
In a particular embodiment, a spring member is interposed between the rocker arm and the piston. More specifically, the rocker arms are each fitted with a spring, preferably a flat spring, positioned so as to be in contact with the end of the associated piston rod and deflecting to allow the pistons to move apart at an increased speed in advance of the crankshaft. The springs are secured and limited so as to provide increasing spring moment as the springs are deflected. This gives rise to a substantial reduction of maximum firing pressure and flattening and extension of cylinder pressure over a wide range of crank angles. Increased thermal efficiency and reduced mechanical friction result in substantially increased Brake Mean Effective Pressure (BMEP).
Two connecting rods are provided, one of which is rotatably attached at one end to each of the rocker arms at a pivot point distal from the rocker arm pivotal mount, and at the other end to a crankshaft which in a specific embodiment is an eccentral containing a power drive gear operatively connected to a drive shaft. The eccentric and power drive gear rotate as the connecting rod pivot point moves up and down due to oscillation of the rocker arm about its pivot point. The second rocker arm is similarly configured. The previously described disadvantages of conventional engines are minimized in an engine of the present invention which provides means for continuously varying the stroke or maximum spaced apart distance of the first and second pistons in each cylinder in accordance with changes in a predetermined performance parameter of the engine, a means for continuously varying the positional relationship of the first piston with respect to the second piston so that blocking an exhaust port by the second piston with respect to the unblocking of a transfer port by the first piston can be altered in accordance with a predetermined engine performance parameter, and a means for defining a combustion chamber which maintains a substantially constant volume during combustion.
The stroke of the engine is adjusted by providing a means for continuously varying during engine operation the pivot point at which each connecting rod is attached to its respective rocker arm, the point of attachment determining the allowable pivotal movement of the rocker arm and thereby the maximum spaced-apart distance of the first and second pistons in each cylinder. By varying the rocker arm pivot point in accordance with engine manifold pressure, a means for compensating for changes in external pressure in order to achieve a predetermined pressure within the combustion chamber at the time of combustion is possible. In addition, the invention discloses a means for manually adjusting the stroke also as the engine is operating, thereby allowing an operator to adjust for differing gasoline octane ratings.
Means for continuously varying the positional relationship of the first piston with respect to the second piston comprises one of the eccentrics forming a shaft having twisted splines on its outer surface, its associated power drive gear being adapted to mesh with the twisted splines so that as the gear is longitudinally displaced along the shaft, it will rotate in accordance with the twisted splines. In operation, as the power drive gear is displaced on the splined shaft, the shaft itself is forced to rotate thereby causing its associated rocker arm to pivot, the other rocker arm remaining stationary. Means are provided to control the longitudinal positioning of the power drive gear on the splined shaft as a function of engine r.p.m., thereby ensuring that the exhaust ports will be closed at the proper time with respect to the arrival of the input air. In addition, the phasing of the first rocker arm with respect to the second rocker arms is chosen so that during the time of combustion both first and second piston surfaces are traveling in substantially the same direction at the same velocity. This ensures that during the time of combustion, the combustion chamber volume is substantially constant.
A remote combustion chamber is also disclosed, the chamber incorporating means whereby direct fuel injection, spark plug ignition or compression ignition can be utilized.